1. Field of the Invention
The present invention relates to a control apparatus which collectively controls an image pickup device and a light source device, and to an imaging system including the image pickup device and the light source device.
2. Description of the Related Art
A conventional CMOS (Complementary Metal Oxide Semiconductor) image sensor often applies a rolling shutter method in which exposure and readout timings change in each horizontal line. The rolling shutter method applies a different exposure timing for each horizontal line in a single picture period, where uneven brightness generated in an image has been a problem when imaging while irradiating with illumination light for only a very short period of time, for example.
When a high-brightness area generated by illumination of the illumination light stretches over two picture periods, an image of the high-brightness area in the picture period being imaged first replaces and corrects a corresponding area in the picture period being imaged later by a known technique, as a technique to eliminate the uneven brightness generated in the CMOS image sensor applying the rolling shutter method (refer to Japanese Laid-open Patent Application Publication No. 2012-19429, for example).
FIG. 19 is a diagram illustrating an example of a relationship between a timing at which pulsed illumination light is emitted and each horizontal line being read in the picture period according to a conventional imaging system. For the convenience of description, it is assumed in FIG. 19 that the number of horizontal lines of an imaging signal equals 18 and that the horizontal lines are read in sequence from the top. In FIG. 19, “VD” indicates a timing at which a vertical synchronizing signal is generated while “HD” indicates a timing at which a horizontal synchronizing signal is generated. Moreover, a horizontal axis “t” in FIG. 19 indicates a time axis.
A readout period In (n=1 to 18) of a frame I (where I is a natural number) indicates a readout period of an n-th horizontal line from the top in the frame I. Similar to the readout period In, each of a readout period Jn of a frame J (=I+1) and a readout period Kn of a frame K (=I+2) indicates a readout period of an n-th horizontal line from the top in the frames J and K, respectively.
In the frame I illustrated in FIG. 19, a pulse is illuminated for the duration equivalent to three readout periods from a readout period I8 as a starting point. Accordingly, the exposure amount in the image corresponding to the imaging signal of each horizontal line being read in the frame I varies according to the relationship between a pulse illuminated period T9I and the readout period in terms of a temporal position. Specifically, the exposure amount in an image corresponding to an imaging signal being read in each of readout periods I1 to I8 all equals zero. Note that the pulse is not illuminated in a frame H (=I−1) in this example. On the other hand, the exposure amount in an image corresponding to an imaging signal being read in each of readout periods I11 to I18 is equivalent to the amount when the pulse is illuminated for the pulse illuminated period T9I. The exposure amount in an image corresponding to an imaging signal being read in a readout period I9 is equivalent to the amount when the pulse is illuminated for a single readout period. The exposure amount in an image corresponding to an imaging signal being read in a readout period I10 is equivalent to the amount when the pulse is illuminated for two readout periods.
An image corresponding to an imaging signal being read in a specified period is hereinafter referred to as an image read in a specified period. Moreover, exposure amount equivalent to the amount when the pulse is illuminated for the specified period is referred to as exposure amount corresponding to the specified period.
Now, an image read in the frame J will be described. The exposure amount in an image being read in each of readout periods J1 to J7 in the frame J corresponds to the pulse illuminated period T9I. On the other hand, the exposure amount in an image being read in each of readout periods J10 to J18 all equals zero. The exposure amount in an image being read in a readout period J8 corresponds to a single readout period. The exposure amount in an image being read in a readout period J9 corresponds to two readout periods.
FIG. 20 is a diagram schematically illustrating an image being read out in the case illustrated in FIG. 19. Images 9I, 9J, and 9IJ in FIG. 20 schematically illustrate the difference in the exposure amount described above by different patterns. This is common to all images illustrated in other drawings.
FIG. 20 illustrates a case where the images 9I and 9J both have uneven brightness. What is performed in the conventional technique in order to reduce the uneven brightness in the image 9J is that an image read in the readout periods J10 to J18 in the frame 9J is replaced by an image read in the readout periods I10 to I18 in the image 9I to create a corrected image 9IJ isuniform excluding the area corresponding to the three horizontal lines in the readout periods J8, J9, and I10, whereby the uneven brightness is reduced compared to the uncorrected image 9J.